Thermoplastic resin films have so broad utility that they have been used in a wide range of technical fields and conditions. Thermoplastic resins such as polyester-based, polyamide-based, polyolefin-based, polyether-based, or polystyrene-based resins deteriorate or decompose by the effect of ultraviolet rays, which results in discoloration and reduction of mechanical strength. Therefore, thermoplastic resins may be detrimental to a long-term usage. Accordingly, various kinds of ultraviolet absorbent have been conventionally used in order to prevent deterioration. Thermoplastic resin films containing ultraviolet absorbents have been used in such a wide range as a window seal, a plastic greenhouse, or protection from insects.
In the areas of inks, medicines and foods, it is known that these goods are deteriorated by a light of ultraviolet range (380 nm or less), or visible short wavelength range (380 nm to 410 nm). However, the subject itself of a film capable of cutting off a specific wavelength has not yet been well known before.
From the past, there are films in which a benzophenone-based or benzotriazole-based ultraviolet absorbent or a metal oxide is incorporated. However, these films had only the ultraviolet absorbing capacity of 380 nm or less, and were unable to absorb light of visible short wavelength region ranging from 380 nm to 410 nm. Resultantly, these films may not have sufficient effect. Further, in some of these films, precipitation or decomposition of the ultraviolet absorbent is caused by heat. Therefore, with respect to some of these films, their ultraviolet absorbing capacity may be down by half during hot forming. Further, some of these films may be unsuitable for hot forming.
Further, it is necessary to add a fairly-high concentration of an ultraviolet absorbent in order to cut off ultraviolet rays over a wide range of from a short wavelength to a long wavelength. However, a simple addition of the ultraviolet absorbent in a high concentration causes problem such as precipitation or bleed-out of the ultraviolet absorbent, arising from a long term use. Further, some of the benzophenone-based or benzotriazole-based ultraviolet absorbents may have properties of skin irritancy or bioaccumulation. Therefore, an extreme caution is required in use.                [Patent Document 1] JP-A-7-11231 (“JP-A” means unexamined published Japanese patent application)        [Patent Document 2] JP-A-7-11232        [Patent Document 3] JP-A-2006-188578        